Conventional plastic mufflers include an outer plastic shell with a metal pipe located within an internal cavity to extend from an inlet to an outlet. These conventional plastic mufflers include packing material that completely fills the internal cavity formed between the metal pipe and the outer plastic shell to provide a fully packed configuration. Packing the internal cavity reduces heat transfer from the internal metal pipe to the outer plastic shell.
While this fully packed configuration provides broadband noise attenuation, it is often desirable to attenuate a specific frequency and/or a limited range of frequencies. Incorporating structure to provide specific noise attenuation characteristics has proved challenging in plastic mufflers.